Microwave scanning antenna system



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Dec. 11, 1956 w. P. BOLLINGER 2,774,067

MICROWAVE SCANNING ANTENNA SYSTEM Filed Aug. 17, 1949 BY Z / ATTORNEYUnited States Patent MICROWAVE SCANNING ANTENNA SYSTEM Waldon P.Bollinger, Haddonfield, N. J., assignor to Radio Corporation of America,a corporation of Delaware Application August 17, 1949, Serial No.110,782

7 Claims. (Cl. 343-762) This invention relates to antenna systems, andmore particularly to a scanning antenna system.

It is often convenient to have an antenna system in which the radiationis lobed, the axis of the lobe being at an angle to an axis about whichthe lobe rotates. Such scanning systems are sometimes termed conicaPscanning systems because the lobe axis describes a cone in itsrevolution about the axis of revolution. Such a conical scanning systemis used, for example, in conventional conical scanning radar sets.

An object of the invention is to provide a particularly simple anddesirable conical scanning system.

It is a further object of the invention to provide an improved means forlobing the radiation pattern of an antenna system at an angle from theaxis of symmetry of the system.

Another object of the invention is to provide a novel conical scanningsystem.

In accordance with the invention, I provide the open mouth radiatingportion of a circular hollow pipe waveguide with two modes of energy atthe same frequency, said modes being excited co-phasally at thewaveguide mouth. The modes are such that the energy of one combinesadditively with the energy of the other on one side of the waveguidemouth and combines in a cancelling manner with the energy on the otherside of the waveguide mouth to give a radiation pattern the lobe axis ofwhich is inclined angularly from the waveguide axis at the mouth.

A further feature of the invention resides in the particularly simplemeans to excite the second mode which may comprise merely a dielectricbody attached to the waveguide inner wall. The section of the waveguidewall which has the dielectric body attached thereto may be rotatablethereby to rotate the lobe. An understanding of the operation and theoryof the invention will be enhanced by consideration of the copendingapplication of Nathaniel I. Korman, Serial No. 766,927, filed September30, 1947 and entitled Antenna Feed System.

The above and other objects, advantages and novel features of theinvention will be more fully apparent from the following descriptionwhen taken in connection with the accompanying drawing in which likenumerals refer to like parts and in which:

Figure 1 is a side view of an antenna system embodying the invention;

Figure 2 is a cross sectional view along the section line 2--2 of Figurel; and

Figures 3 and 4 are cross sectional views along the section line 33 ofFigure 1 illustrating the electric vectors of modes which may bepropagated in the waveguide.

Referring now more particularly to Figure 1, a hollow pipe waveguide ofcircular cross-section (circular waveguide) has an open mouth 12 adaptedto radiate energy. The waveguide has a suitable inner diameter to permitpropagation of the TMo,1 and the T E1,1 modes. A lens system, forexample, of the suitably curved dielectric type, schematicallydesignated by the reference 2,774,067 Patented Dec. 11, 1956 numeral 14,is placed with its focal point substantially at the waveguide mouth 12.A scanning motor 16 drives a waveguide section 18 through suitablegearing 20 to rotate said section about its longitudinal axis. Thesection 18 of waveguide 10 has attached to its inner metallic wall adielectric body or block 22 which is assymetric with respect to thelongitudinal axis of the waveguide 10. A transducer 24, which may be agenerator or receiver of high frequency waves, supplies or receivesenergy to or from waveguide 10 preferably in the TMo,1 mode. Theoperation will be considered with transducer 24 as a generator, and theconverse operation if it is a receiver will then also be clear to thoseskilled in the art.

Figures 3 and 4 illustrate by vectors 26 and 28 respectively theconfiguration of the electric vectors in the TE1,1 and TMo,i modespropagated through waveguide 10. Transducer 24 may generate energyentering waveguide 10 in the TMo,1 mode. As the energy approaches thesection 18, and strikes the dielectric block 22, which preferably hastapered end portions 22a to reduce reflections, the TE1,1 mode is alsoexcited, as illustrated by vectors 26 in Figure 3. The amount of energywhich is so excited will depend upon the length, size, and configurationof the block 22. The energy proceeds down waveguide 10 toward the mouth12, the distance between the section 18 and the mouth 12 beingcalculated so that, due consideration being given to the phasevelocities of the energy excited in each mode, the energy will reach themouth with the modes substantially in phase. Accordingly, when thevectors 26 have reached their maximum amplitude, so also have thevectors 28 at the mouth of the guide. It will be apparent that the twoenergy configurations are vectorially added.

Since the two modes have different types of symmetry, the TE1,1 modehaving substantially even symmetry about a central vertical plane andthe TMo,1 mode having substantially odd symmetry about a centralvertical plane, at least at the central horizontal axis, it is apparentthat the total energy leaving the mouth of the guide will have electricvectors of larger amplitude on one side than on the other. A half cyclelater the vectors 26 will have reversed direction, and also the vectors28, so that the same side which had larger vectors a half cycle prioragain has larger vectors. The relationship between these modes may stillbe simply described as co-phasal, since each reaches maximum amplitudetogether, even though on one side of the central vertical plane thevector signs or directions are opposed. The energy so radiated will tendto travel off in a lobe the axis 30 of which is inclined at an angle tothe waveguide axis 32. The lens 14, in accordance with well-knownmicrowave optical principles, may increase the angular inclination ofthe axis 30 in a manner schematically represented by the axis 30'. Asthe scanning motor 16 turns section 18 and dielectric block 22 isrotated therewith, the radiation axis 30' will rotate about the centralaxis 32, thereby providing conical scanning. The section 18 may bejoined to the waveguide portions on either side thereof by the usualchoke joints (not shown) in a manner well known to the art. Also itshould be noted that other means than the dielectric block section ofwaveguide are well known in the art for effecting a transfer of energyfrom one mode, say the TMo,1 to another, say the TE1,1 and these mightalternatively be used. I have here shown what I consider a preferredform of the invention.

Having thus described the invention as a particularly simple system forproducing a conical scan and which comprises a circular waveguide inwhich two modes of different symmetry leave the mouth thereof in phaseto obtain a lobe the axis of which is inclined to the axis of thewaveguide and having shown how rotation of the lobe axis about thewaveguide axis is readily derived, what I claim as my invention is:

1. In a scanning antenna system, a circular hollow pipe waveguide havinga throat portion and having an open mouth portion for radiation orreception of electromagnetic energy, said portions having a longitudinalaxis and having transverse dimensions to propagate at an operatingfrequency a first mode having components of odd symmetry with respect toa plane passing through and containing said axis and to propagate energyat said frequency in a second mode having components of even symmetrywith respect to said plane, means comprising a section of said Waveguidebetween said throat and said mouth portions to couple such energy ineach of said modes in said mouth portion to such energy in one only andnot the other mode in said throat portion with said coupled energy insaid two modes in the mouth portion being co-phasal at the mouth therebyto direct the principal axis of the directive energy pattern of saidmouth portion to one side of said plane, and means to move said couplingmeans around said axis, whereby the position of said plane is moved andsaid principal axis of said radiation is moved around said axisextended.

2. In a scanning antenna system, a circular hollow pipe waveguide havinga throat portion and an open mouth portion for radiation or reception ofelectro-magnetic energy, said portions having a longitudinal axis andhaving transverse dimensions to propagate at a given operating frequencythe TE1,1 mode and the TMu,1 mode, means in a section of said Waveguidebetween said throat and mouth portions to couple between said portionssuch energy in each of said modes in said mouth portion to such energyin the said TM0,1 mode only and not the other said mode in said throatportion, said coupled energy in said two modes in said mouth portionbeing cophasal at the mouth thereby to direct the principal axis of thedirective energy pattern of said mouth portion to one side of saidplane, and means to move said means in said section around said axis,whereby the position of said plane is moved and said principal axis ofsaid pattern is moved around said axis extended.

3. The system claimed in claim 2,,further comprising a lens with saidwaveguide mouth substantially at the focal point thereof.

4. The system claimed in claim 2, further comprising a transducercoupled to said circular waveguide at an end thereof remote from saidmouth and coupling to energy solely in said TMo,1 mode and not in theother mode in said throat portion.

5. In a scanning antenna system, a circular hollow pipe waveguide havingmetallic walls enclosing a dielectric medium and a throat portion, amouth portion to radiate or receive electro-magnetic energy at theoperating frequency, and a section between said throat and mouthportions, said waveguide having a longitudinal axis and havingtransverse. dimensions to propagate such energy in the T Mc,1 mode andto propagate such energy in the TE1,1 mode, said section having adielectric body movable about said axis attached to the inner waveguidewall of different dielectric constant from the medium enclosed withinthe waveguide walls, said body being asymmetrical with respect to thesaid waveguide axis, said section coupling between said mouth portionand said throat portion such energy in the throat portion in the TMo,1mode only and not in the TE1,1 mode with energy in each of said modes inthe said mouth portion co-phasal at the mouth, thereby causing theprincipal axis of the directive energy pattern of said mouth portion forsuch energy to have an angle with the said waveguide axis extended.

6. The system claimed in claim 5, said waveguide section and saiddielectric body being rotatable, thereby to rotate the said principalaxis of said pattern about the waveguide axis extended.

7. The system claimed in claim 5, further comprising a dielectric lenssystem with said waveguide mouth positioned at the focal point of saidlens system.

References Cited in the file of this patent UNITED STATES PATENTS2,129,669 Bowen Sept. 13, 1938 2,283,568 Ohl May 19, 1942 2,433,368Johnson et a1 Dec. 30, 1947 2,473,446 Riblet June 14, 1949 FOREIGNPATENTS 582,856 Great Britain Nov. 29, 1946 OTHER REFERENCES Theory andApplication of Microwaves, by Bronwell and Beam; Mc-Graw-Hill Book Co.,1st ed. 2nd impression, 1947 ch. 18.

